If you run your mains full-range, and assuming they have bass response to at least 30Hz, they may very well improve bass smoothness in your room. The more bass sources you have the more room modes are generated (dips and peaks in the perceived output level in the room). The more modes you generate the better they average things out.
With some speakers, especially those with relatively small woofers crossed over well into the midrange, relieving them of reproducing the bass frequencies may improve the overall sound more than increasing the number of room modes, especially if you have the flexibility to place the sub for best bass response, or you can use multiple subs.
I've tried several different alternatives in my system, and I'm currently running the mains full-range, but with a reduced bass setting on the so-called contour switch on the speakers, and I use a 120Hz low-pass filter on the sub, with appropriate equalization to cut some peaks. I also had good luck with a 60Hz low-pass filter with a shallow 6db/octave slope, and an 80Hz high-pass filter for the main speakers. I moved away from using the high-pass filter only because the sub's input was overloading on some passages, and distorting the feed to the primary amps.
In the end I think bass at my listening seat is best with the mains running full-range. Because my mains reach down into the sub-20Hz range it's like having three subs in the room.
With some speakers, especially those with relatively small woofers crossed over well into the midrange, relieving them of reproducing the bass frequencies may improve the overall sound more than increasing the number of room modes, especially if you have the flexibility to place the sub for best bass response, or you can use multiple subs.
I've tried several different alternatives in my system, and I'm currently running the mains full-range, but with a reduced bass setting on the so-called contour switch on the speakers, and I use a 120Hz low-pass filter on the sub, with appropriate equalization to cut some peaks. I also had good luck with a 60Hz low-pass filter with a shallow 6db/octave slope, and an 80Hz high-pass filter for the main speakers. I moved away from using the high-pass filter only because the sub's input was overloading on some passages, and distorting the feed to the primary amps.
In the end I think bass at my listening seat is best with the mains running full-range. Because my mains reach down into the sub-20Hz range it's like having three subs in the room.